Fluid samples are often introduced to process analyzers with valves that provide a fixed amount of sample. Some process analyzers require a continuous, constant flow of sample. This can be achieved by ensuring that the flow rate of the sample remains constant while it is being introduced and processed by the analyzer. One way to achieve a constant flow rate is by passing a stable viscosity sample through a restrictor at constant pressure. This will not work for a sample whose viscosity is changing unpredictably. Any change in the composition of the fluid sample can result in a change in viscosity, and, hence a subsequent change in its flow rate through the restrictor. The nature of flare samples is that they frequently undergo unpredictable and dramatic compositional changes. This dramatic variation in the composition of the flare lines and the resulting changes in viscosity can make the control of the flow rate of a sample of flare line gas a difficult problem.
Ulrich Gokeler and Friedhelm Müller, in “On Line Monitoring Of Total Sulfur In Combustion Fuel Using Process Gas Chromatography”, 2001 ISA Analysis Division Proceedings, Houston, Tex., October 2001, the disclosure of which is incorporated herein by reference, describes an analytical system for an automatic online total sulfur analyzer based on a proven process gas chromatographic technique utilizing a new and unique system to vaporize small amounts of sample continuously. The vaporized sample is continuously burned in a Flame Ionization Detector (FID) flame to produce, various components of the sample, such as, for example, sulfur dioxide, water and carbon dioxide. The sulfur dioxide, represents the entire sulfur content in the sample, which is then separated using conventional gas chromatography and detected utilizing a Flame Photometric Detector (FPD).
U.S. Pat. No. 6,453,725 (Robert W. Dahlgren, et al.), the disclosure of which is incorporated herein by reference, discloses a multi-port, diaphragm sealed valve suitable for use as both a sampling and column switching valve. The valve is constructed to internally block fluid communication between one or more pairs of ports in a valve operating mode. Such blocking may be used to conserve carrier gas when the valve is in the ON position.
Even with these improvements, a need exists for an improved apparatus and method for fluid sample introduction.
Thus, a need exists for a method and an apparatus for a continuous, constant flow, sample introduction for compositionally unstable fluids.
A need also exists for associating at least one fluid analyzer system with an apparatus for a continuous, constant flow, sample introduction.
This invention also overcomes the problems of the prior art. The invention provides a method and an apparatus for an automatically compensating continuous, constant flow, sample introduction system.